Restricting vertices to a 3D grid
Are you perhaps talking about the Snap to Grid tools? 

You simply click to the magnet icon to enable that, pick your poison in terms of what you want to snap by (side-note: doing so by volume is fantastic when setting up rigs). Works in object/edit modes, and with all sorts of translation/scaling/rotating.

Edit: If you want to modify the increment size, try this answer.



Hope that helps!